Method for the concentration and separation of metals



July 3, 1962 E. J. SCHUMACHER METHOD FOR THE CONCENTRATION AND SEPARATION OF METALS Filed Oct. 13, 1959 5 Sheets-Sheet l 3mm t'rnsf Joseph Schumac/rer Fig. 1a

Fig. 1b

July 3, 1962 E. J. SCHUMACHER METHOD FOR THE CONCENTRATION AND SEPARATION OF METALS Filed Oct. 13, 1959 5 Sheets-Sheet 2 fi-ns/ Jasepb Schumac/rer 2%, MM, zlzkflpm uma Eve 3%. W fidm O i i s 37 NN/ I July 3, 1962 METHOD FOR THE CONCENTRATION AND SEPARATION OF METALS Filed Oct. 13, 1959 5 Sheets-Sheet 3 Fig. 9

3mm fmsf Jaseph Schumacher wn/M, MaAPdw/a y 1962 E. J. SCHUMACHER 3,042,597

METHOD FOR THE CONCENTRATION AND SEPARATION OF METALS Filed Oct. 13, 1959 5 Sheets-Sheet 4 I )1 H o 5 3 llz ,\.\\\r #52 1| "M a July 3, 1962 E. J. SCHUMACHER 3,042,597

METHOD FOR THE CONCENTRATION AND SEPARATION OF METALS Filed Oct. 15, 1959 5 Sheets-Sheet 5 'n In I 3mm t'rns/ Joseph SIM/mother Wh/MJ United States atent 3,042,597 METHOD FOR THE CONCENTRATION AND SEPARATION OF METALS Ernst Joseph Schnmacher, Ruschlikon, Zurich, Switzerland, assignor to J. R. Geigy A.-G., Basel, Switzerland Filed Oct. 13, 1959, Ser. No. 846,1 3 Claims priority, application Switzerland Jan. 31, 1957 12 Claims. (Cl. 204-180) The present invention relates to a process for the concentration of metals and the separation of mixtures of metals in form of homogeneous solutions of their ions in a dielectric under the action of an electrical field. The invention also relates to mechanical devices either alone or combined with each other, which are used for the new method of concentration or separation in the field of analytical, preparative or technical chemistry. This application is a continuation-in-part of application Serial No. 712,458, filed January 31, 1958, now abandoned.

Electrophoresis is also an electrical separation method which is often used in the art. It is based on the fact that the velocities of travel of ions of difierent size and charge in a solution of fixed viscosity are different in a given electrical field. In the case of relatively long action of the field, electrophoresis leads to an excellent separation of ions of opposite charge and is especially useful in the separation of proteins. For the separation of simple metal ions electrophoresis, however, is less suitable because these ions move in the same direction under the influence of the electrical field. Thus only the very small difierences in migration, velocity between the individual metal ions can be utilized to effect separation.

It has now been found that the ions of different metals can be satisfactorily separated in solution in a fluid dielectric under the influence of an electrical field when there is used, not the velocity of travel of the ions as the means of differentiation, but the stability of their complex particles.

It is well known that upon addition of a small amount of complexing agent to a solution of different metal ions only the complexes of the metal ion forming the most stable complexes are formed. Further addition of the complexing agent will then produce complexes of the metal having the second highest complex stability and so on. The metal ions present in the solution are complexed in the order of decreasing numerical value of the complex stability constants. The process according to the present invention now uses this principle of successive complex formation to cause a simultaneously occurring spatial separation of said metals.

The new method of separation according to the present invention is characterized by the simultaneous separation of metals in form of their solutions in a fluid dielectric containing molecularly dissolved metal-containing anions and cations derived from said metals, which dielectric is located in the space inbetween two electrodes and is restricted from free convection by inert ion permeable structures and contains a concentration gradient of a complexing base which takes part in the rapid interconversion of the cationic and anionic fractions of the particles containing said metals, by the application of an electrical field of the same direction as the spacial increase in concentration of said complexing base, whereby all the metal containing particles of said metals are collected in the individual small zone of the electrode interspace corresponding to the individual zone for each metal in which substantially half of it metal-containing particles are in the anionic form, whereupon the liquid contents of said different zones are mechanically separated from the rest of the liquid content of the electrode interspace and hence from each other.

According to a modification of the process of the present invention at least one more concentration gradient of a further complex forming base is created, which base forms stronger complexes with at least one of the metals to be separated, the amount of the further complex forming compound being at least equivalent to the amount of the metal forming the stronger complex.

The known electrophoretical methods allow separation of certain metal containing particles but are not capable of increasing the concentration of the metals above and over the concentration at which the metals are present in solution prior to subjecting them to such conventional electrophoresis. In distinct contrast thereto, the new method of separation according to'the present invention is capable of increasing the concentration of the metals present in solution so that after performed operation, more concentrated solutions are obtained than have originally been entered into the process. It is, therefore, a further objective of the present invention to concentrate dilute metal solutions and it is characterised by the concentration of metal-containing cations and anions derived from one and the same metal dissolved molecularly in a fluid dielectric which is located in the space inbetween two electrodes, said dielectric being restricted from free convection by inert ion permeable structures and containing a concentration gradient of a complexing base which takes part in the rapid interconversion of the cationic and anionic fractions of said metal-containing particles present, by the application of an electrical field of the same direction as the spatial increase in concentration of said complexing base, whereby all metal-contain ing particles-are collected in the small zone of the electrode interspace in which substantially half of the rnetalcontaining particles are in the anionic form.

FIG. 1a is a sectional elevation view of an apparatus for carrying out the process according to the invention;

FIG. lb is a plan view of the apparatus of FIG. In;

FIG. 10 is a perspective view of a part of the apparatus of FIG. 1a;

FIG. 2 is a plan view of a piece of filter paper used in the apparatus of FIGS. la-lc prior to the application thereto of an electric field;

FIG. 3 is a plan view of a piece of filter paper used in the apparatus of FIGS. la-1c after the application of an electric field;

FIG. 4 is a plan view of a piece of filter paper used in the apparatus of FIGS. la-lc with the solution of metals to be separated applied to the filter paper in a different way from FIG. 2;

FIG. 5 is a schematic plan view illustrating the manner in which a constant flow apparatus for carrying out the process according to the present invention will work;

FIG. 6 is a plan view of a base plate of one form of an apparatus which will operate continuously to separate metals in solution by the method according to the present invention;

FIG. 7 is a sectional view of a top plate for such an apparatus;

FIG. 8 is a exploded sectional view of the housing for the separation chamber of such an apparatus;

FIG. 9 is a schematic plan view of the separating means of such an apparatus showing the electrical connections therefor;

FIG. 10 is a perspective view, partly in section of such an apparatus in the assembled condition; and

FIG. 11 is a schematic view, partly in section of the over-all apparatus.

In the description and in the following claims, by particles is always meant a simple ion or a molecularly soluble atom grouping. As such, this atom grouping can be uncharged, i.e. it is a neutral molecule; it can be positively charged, i.e., it is a cation, or it can be negatively charged, i.e., it is an anion. In this connection, particle never means a solid microscopic body.

Molecularly dissolved means that the particles cOn cerned are soluble and form a true solution, possibly forming a solvate and that they do not aggregate to form structures of higher order such as occur in colloidal solutions and dispersions.

In the description and the following claims, concentration gradient should be understood as to mean the spatial inequality of the concentration In the present invention, generally a concentration gradient is essential in which a spatially variable concentration exists parallel to the field vector of the electrical field. In the planes perpendicular to this field vector however, a substantially constant concentration should exist.

Mathematically, grad 0 should have no or only very small components perpendicular to the electrical field vector, the component parallel to said vector should have a finite value different from 0. These mathematical terms are important for theoretical considerations only, since in practice the concentration relationships including the concentration gradient are properly formed automatically under the influence of the electrical field using the practically preferred conditions. For the reciprocal intercorrelation of the concentration and the location. in the electrode interspace, said grad c is a very practical means.

Water is chiefly used as liquid dielectric. Dilute aqueous solutions of methanol, ethanol, propanol, etc. can also be used. Under special conditions the use of dimethyl sulphoxide, dimethyl formamide and similar high power solvents in the dielectric can also be considered.

It is to be understood that the actual solutions in which concentration and separation take place have to be electrical conductors but that the electrical conductivity does not stem from the liquid dielectric per se but from the ions dissolved therein.

Ion permeable inert structures which can be used in the sense of the present invention to restrict the liquid contents of the electrode interspace from free convection can be evenly distributed within this interspace or they can subdivide said electrode interspace into appropriate chamber or canal systems in the form of bands and layers. Such ion permeable inert structures can be built from any inert ion permeable material desired. In practice however, cellulose derivatives in the form of any paper pulp product like filter paper or cardboard, porous structures from cellulose acetate and similar cellulosic esters, asbestos fibre products, glass fibres, sintered glass plates, porous ceramic plates and inert plastic fibres or structures are preferred.

By free convection is meant the uncontrolled intermixing of adjacent liquid elements due to difierences in temperature, static and hydrodynamic pressure within said elements or external mechanical means.

The terms acid and base are used throughout this description and in the claims in the sense of the'modern Brrzinsted and Lewis definition, i.e. a base is a particle capable of adding a proton or any other electrophilic particle such as borontrifiuoride or Cu II ions, and an acid is a particle capable of reacting with an aforementioned base by delivering a proton to it or by direct addition to it.

from said complexing agent which can be replaced ultimately by, metal during complexing reactions. A complexing base, therefore, is the particle which can be united with a metal ion directly without splitting off of protons.

In order for a complexing agent to be useful according to the present invention, it must be a proton acid, i.e. it must be able to give off protons during the complexing process. The most diverse inorganic and organic acids can be used as source for the complexing bases provided they themselves and their salts are molecularly soluble in the dielectric used. The choice of appropriate complexing bases in order to solve a specific task will be discussed below.

The following list gives examples of complexing agents as sources of complexing bases which can be used according to the present invention:

Inorganic acids such as: hydrochloric acid, hydrofluoric acid, thiocyanic acid, carbonic acid; phosphoric acids such as .pyrophosphoric acid and trimetaphosphoric acid.

Organic acids such as: aromatic carboxylic acids, for example benzoic acid and toluic acid, aliphatic and hydro-aromatic acids, for example acetic acid, chloroacetic acid, oxalic acid, succinic acid, maleic acid.

Hydroxycarboxylic acids of the aliphatic, aromatic and hydro-aromatic series, for example, lactic acid, gluconic acid, tartaric acid, citric acid, salicylic acid, sulphosalicylic acid, l-hydroxy-cyclohexane carboxylic acid-1.

Aminocarboxylic acids of the aliphatic, aromatic and hydro-aromatic series, for example, glycine, fi-alanine, imino'diacetic acid, nitrilotriacetic acid, ethylene diamine tetra-acetic acid, aniline diacetic acid, anthranilio acid, anthranilic acid-N-diacetic acid, 1.2-diaminocyclohexane tetra-acetic acid.

Aminohydroxycarboxylic acids, for example, hydroxyethyl-ethylene diamine triacetic acid, bis-(B-hydroxyethyl)-g1ycine, N.N-bis-(p-hydroxyethyl) 'anthranilic acid, N-(Z-hydroxycyclohexyl)-ethylene diamine triacetic'acid.

Phenols, for example, pyrocatechol, pyrocatechol disulphonic acid, chromotropic acid.

Heterocyclic acids, for example, 8-hydroxyquinoline-5- sulphonic acid.

In the most general case an appropriate neutral compleXing molecule corresponds to the formula H B which can form a complexing base B- by giving off a maximum of b protons in the solvent system used.

According to the following equilibria, this molecule H B can dissociate otf protons or can add protons whereby all particles H B are in mutual equilibrium and exist as such even if only in very minor concentration.

H B +iS=B- +iHS+; A,

In these formulae S represents the solvent molecule, A represents the equilibrium constant of the above reaction having the value:

1 0 )(H yfl rm i represents a whole number which can have the values of 1,2,..b...b+n,

n represents the number of protons which the molecule H B can add while forming anionic particles,

B" represents the complexing base corresponding to the complexing agent molecule H B which is characterized in that it does not give off any protons upon reaction with metal ions when forming complex ions,

H B represents the particle of the degree of protonation of the complexing base, i.e. the particle which is formed from the complexing base ]3 by the addition of i protons. In the case of i b this particle is an anion to which salts correspond such as Na [H B] etc. In the case 5:1), this particle is identical to the complexing agent molecule H 3 and in the case i b, this particle is a cation to which salt corresponds such as [H;B]C11 6116.

This complexing base B is of prime importance because the degree of complex formation with a metal is directly related to its concentration. B is the one particle the concentration of which has to vary spatially accorcling to the present invention.

The concentration of 13- can be rendered high by addition of a base such as sodium hydroxide, to a solution of the complexing molecule H B. On the other hand, a low concentration of 3- is obtained by addition of a complex destroying agent which is a strong acid in the sense of the above definition. The term complex destroyer is employed to express the capability of such an agent to destroy pre-formed complexes due to the lowering effect on the B- concentration.

It is immaterial whether the concentration gradient with respect to the complexing base B' is arrived at by spatial variation of the total concentration of the complexing agent molecule H B at constant complex destroyer concentration, e.g. protons (constant pH) or by appropriate variation of the pH or the concentration of other complex destroyers, such as Fe III ions while maintaining a constant total concentration of the complexing agent molecule or by simultaneous spatial variation of the above mentioned factors which, in practice, will generally co-operate in the formation of the necessary complex base concentration gradient The technically most simple means to create favourable conditions for the formation of said gradient consists in introducing the complexing base into the cathode compartment and the complex destroyer into the anode compartment. Under the influence of the electrical field, the complexing base will leave the cathode compartment and enter the electrode interspace which is restricted from free convection of its liquid contents. Obviously the parts of the electrode interspace next to the cathode compartment will so contain higher concentrations of cornplexing base than the parts further removed from the cathode compartment.

in a preferred embodiment of the present invention, a solution of a complex destroyer is filled into the anode compartment. Under the influence of the electrical field the highly acidic particles of the complex destroyer such as protons or strongly acidic metal ions, exemplified by ferric and cupric ions, move into the electrode interspace and destroy there the complexing base, thus lowering its concentration. Again this effect of the complex destroyer is not the same throughout the electrode interspace but is most pronounced in the vicinity of the anode compartment. The complex destroyers thus take an active part in the formation of the essential concentration gradient of the complexin g base.

Examples of useful complex destroyers are: hydrochloric acid, nitric acid, sulphuric acid, phosphoric acid, hydrofluoric acid, perchloric acid, hydrogen tetrafluoroborate, trifiuoroacetic acid, ferric ions in form of the ferric perchlorate, nitrate, chloride, cupric ions in the form of cupric sulphate, chloride, nitrate and zirconium per chlorate.

The most simple mode of operation of the present invention is best illustrated and explained by the analytical The apparatus con- (a) The anode compartment 1 containing the complex destroyer solution 2 and the anode 3,

(b) The cathode compartment 4 containing the complexing agent solution 5 and the cathode 6.

(c) A filter paper strip 7 which connects these two electrode compartments and part of which represents the electrode interspace in which the concentration gradient with respect to the complexing base exists and the actual concentration and separation of the metals is performed. in order to minimize evaporation of the liquid contained in the filter paper strip 7 the strip is immersed in a non-conductive cooling liquid 8 con taiued in a cooling compartment 9 by means of holder lit. This cooling liquid is immiscible with the dielectric fluid used in the metal solution as well as in the electrode compartments.

The actual mode of operation in the analytical apparatus is as follows:

A solution of the metals to be concentrated and/0r separated in the liquid dielectric is applied near the middle portion of the dry filter paper strip (7 of FIG. 1). One end of this strip is then immersed in the anode and the other in the cathode liquor. By the capillary action of the filter paper the electrode liquors are sucked into the body of the strip. As soon as they reach the zone wetted by the metai solution from each side, the strip is immersed into the cooling liquor and a DC current is applied to the electrodes. As explained above, a concentration gradient of the complexing base is established in the electrode interspace. The spatial increase of the concentration of the complexing base (i.e. the concentration gradient) has the same direction as the electrical field applied.

Under the influence of the electrical field, all regions of the solution within the electrode interspace characterized by low complexing base concentrations will be depleted of metal because the metal-containing cations originally present or formed during the process will travel towards the cathode, i.e. in direction of increasing concentration of complexing base. The total fiow of metal in such regions is thus in the same direction as the electrical field. the same way, the regions of high complexing base concentration will be depleted of metal because the metalcontaining complex anions originally present or newly formed during the process will travel towards the anode, i.e. in the direction of decreasing concentration in complexing base. The total flow of metal in such regions is thus in the opposite direction to the electrical field. At that zone of the electrode interspace where the two metal streams meet and into which the metal is transported in the form of equal fractions of cations as well as anions, all the metal will accumulate. In this very limited zone of the solution within the electrode interspace, all the metal is present after completion of the operation and is amenable to isolation in the form of its solution.

This process of concentration will be referred to as focussing of the metal and the zone of accumulation of the metal will be referred to as the focus. The focus of the metal within the concentration gradient of the complexing base is located in the area of the electrode interspace into which the number of anionic metal particles immigrating from the cathode side per time unit equals the number of cationic metal particles immigrating from the anode side per time unit. Since the absolute value of the migration velocity of the different metal-containing particles is very similar, the focus will occur where the concentration of the complexing base is such as to produce essentially equal amounts of all possible cationic and all possible anionic metal particles. This characteristic value of the complexing base concentration at which the focus is produced is designated as (B This (B- depends directly and normally solely upon the complex stability constant characteristic of the metal complexing base combination in question. For example, in the case of the system cupric ions-nitn'lo triacetic acid, the anionic metal-containing particle CuB- is formed. B stands for the complexing base N(CH COO-) and the stability constant of CuB- is defined by the following equation: K=l (CuB)/(Cu)(B). The copper containing ions are focussed where (CuB)/(Cu)-l. The (B-) characteristic for the focus of copper in a nitrilotriacetate concentration gradient is therefore (B) =l0 For cobalt on the other hand, the complex stability constant amounts to K=l0 and the (B characteristic for the cobaltous focus in the nitrilotriacetate concentration gradient is (The values of the complex stability constants K are taken from Special Publications, Nos. 6 and 7, The Chemical Society, London, Burlington House, W.l., 1957; Stability Constants of Metal-Ion Complexes, compiled by Jannik Bjerrum, Gerold Schwarzenbach and Lars Gunnar Silln.)

The phenomena described above are illustrated in FIGS. 2 and 3. In FIG. 2 the filter paper strip 7 is shown prior to its immersion into the cooling bath and the onset of the electrical field. Section (c) of the strip is wetted with the solution of, e.g. two metals to be concentrated and separated, and represents the electrode interspace. Sections (:1) and (e) are the parts of the filter paper strip which are immersed into the anode and cathode liquors respectively. Sections (b) and (d) are those parts of the filter paper strip into Which the anode and cathode liquors respectively penetrate due to the capillary action of the filter paper thereby forming a liquid junction between the electrode compartments and the electrode interspace. FIG. 3 shows filter paper strip 7 after termination of the concentration and separation under the influence of the electrical field. Sections (a), (b), (c), (d) and (e) have the same meaning as in FIG. 2. The two diilerent metal ions originally evenly distributed in the whole of the electrode interspace (c) are now accumulated in the two small zones (foci) f and f of the electrode interspace (c) respectively. The distance of the two foci from each other depends upon the specific mode of operation as illustrated in the specific examples. 7

It is not necessary, however, that the metals to be sep arated are evenly distributed in the electrode interspace (section (0) of filter paper strip 7 of FIGS. .2 and 3) prior to the separation. As shown in FIG. 4 they can be so applied as to occupy only part of the electrode interspace. In this case, the solution of the metals to be separated is applied to section (g) of filter paper strip 7 whereupon the remainder of the electrode interspace (c) is wetted, e.g. with a dilute solution of an inert salt, such as alkali metal salts of strong mineral acids, e.g. sodium chloride, not interfering with separation, in the same liquid dielectric as is used for dissolving the metals and as used in the electrode liquors. Under the influence of the electrical field, the concentration gradient of the complexing base is formed and the metals are again focussed into two foci f and f analogously to FIG. 3.

The complexing agent contained in the cathode liquor has to be present in large excess over the metals to be separated, is. in at least ten to fifty fold the equimolecular amount. This complexing base contained in the cathode liquor will be referred to in the following as the primary complexing agent and the corresponding complexing base which forms the essential concentration gradient in the electrode interspace will be referred to as primary complexing base.

In the practice of the present invention, it is often desirable to use additional complexing agents. Such additional complexing agents can have two distinctly different actions.

On the one hand they have auxiliary functions. They merely impart specific and desirable properties to the particles to which they add themselves. Such properties can be an electrical charge, a specific solubility in the dielectric used or a special stability in a pH region otherwise leading to malfunctions. Additional complexing agents of such character are referred to in the following as auxiliary complexing agents and need not necessarily be capable of producing anionic complexing bases. Examples of such auxiliary complexing agents are the compounds listed in column 4, lines 2753, provided that they form less stable complexes than the primary complexing agent chosen in the specific mode of operation, as well as amines such as ammonia, methylamine, triethylamine, cyclohexane diamine-1.2, pyridine, o-phenanthroline, 1.3- diketones.

They can be added in the cathode compartment or in the electrode interspace or in form of their metal complexes of the metals to be separated.

On the other hand, such additional complexing agents take part actively in the focussing of the metals to beseparated. They are responsible for the focussing of part of these metals whereas the remainder of the metals is focussed by the primary complexing agent. Complexing agents of such character are referred to in the following as secondary complexing agents and their corresponding complexing base as secondary complexing base. These secondary complexing agents are added in amounts substantially equivalent to the amount of the metals which they focus. They are also distinctly different from the primary complexing agents in that they do not have to be added necessarily to the cathode compartment but can be added to the electrode interspace in form of their metal complexes of the metals to be separated. In contrast to the auxiliary complexing agent, the secondary complexing agents must form anionic complexing bases of which a concentration gradient has to exist at least in that part of the electrode interspace inbetween the anode compartment and the place of addition of the metal solutions to the electrode interspace. As secondary complexing agents the same compounds can be used which have been listed as useful primary complexing agents, provided that they form more stable complexes with the metals to be focussed by them than the primary complexing agent used in the specific operation. This is in further contrast to the auxiliary complexing agents.

The action of a secondary complexing agent is characterised by the fact that its use leads to a double concentrating elfect or focussing for one and the same metal. If, for example, cupric chloride solution is applied to the filter paper strip 7 of FIG. 1 and 0.5 N hydrochloric acid is used as'complex destroyer and a solution which is 1.0 N with respect to sodium acetate and 0225 N with respect to acetic acid is put into the cathode compartment, the focussing of the copper under the influence of electrical field causes the formation of a focus less than 1 mm. in width which contains all the copper. This zone of the electrode interspace will be referred to as acetate focus. If now, a small quantity of nitrilotriacetic acid is added to the copper dichloride solution applied to the filter paper strip and the metal is focussed as before, two distinctly different foci are formed. The acetate focus appears at its original place, but about 12 mm. nearer to the anode a new focus is found which is due to the nitrilotriacetic acid and will be referred to as nitrilotriacetate focus. The two complexing bases thus act independently of each other. Closer examination of the phenomenon has shown that thenitrilotriacetate focus (i.e. the focus of the secondary complexing agent) contains an amount of copper equivalent to the amount of nitrilotriacetic acid added, and that the amount of copper contained in the acetate focus (i.e. the focus of the primary complexing agent) is reduced by this amount. vNow, the addition of an amount of nitrilotriacetic acid equivalent to the total amount of copper present causes the complete disappearance of the original acetate focus. Again only one focus appears,

1&7 namely the nitrilotriacetate focus lying closer to the anode than the acetate focus. This phenomenon is subsequently referred to as complete double focussing.

As already mentioned, the formerly discussed auxiliary complexing agents are characterised by a complete lack of such double focussing. Between the two extremes, the complete double focussing and the absence of double focussing, lies the incomplete double focussing. This is the phenomenon characterised by the fact that even in the presence of an amount of secondary complexing agent equivalent to the metal, two foci are formed. This phenomenon is, of course, only quantitatively different from the complete double focussing, but is qualitatively different from the action of the auxiliary complexing agents.

Double focussing is of interest in cases in which a specific primary complexing agent causes the formation of sharp foci lying closely together so that a clean mechanical separation of the metals contained in these foci is doubtful. Focussing of the metals at places lying further apart is then effected by means of a concentration gradient of a secondary complexing agent whose complex stabilities are such as to produce double focussing with only one of the metals and which secondary complexing agent is used in an amount equivalent to said metal. The other foci appear at their original place but the completely double focussed metal appears apart from them nearer to the anode. In the case of two metals to be separated, this leads to a clean separation of the two. If more than two metals are present, it is possible to remove one metal after the other from its original place by double focussing. In this case an amount of the secondary complexing agent equivalent to the metal forming the most stable complex is first used, the operation is performed under the influence of the electrical field and said metal is isolated at its new focus. Then an amount of secondary complexing agent equivalent to the metal forming the second most stable complex is added, the metals are focussed and the second metal is isolated from its new focus and so on.

Double focussing not only allows better separation of otherwise difficultly separable metals but it also gives advantages in economy. In the vast majority of cases proper choice of the primary complexing agent allows clean separation of a specific metal combination. Quite often, however, expensive compounds have to be used to per form the task. It is, therefore, much more advantageous to use very cheap primary complexing agents like, for example, sodium acetate and to improve the separation effected by them by use of more powerful but more expensive secondary complexing agents for example nitrilotriacetic acid or ethylene diamine tetra-acetic acid in quantities equivalent to the metals to be double focussed.

The concentration gradient of the secondary complexing base can be produced simultaneously with or separately from the production of the concentration gradient of the primary complexing base. It can again be formed mechanically or by the action of the electrical field used in the separation of the metals. The latter method is generally preferred. In this case, the secondary complexing agent may be added directly to the solution containing the metals to be separated.

In practice, such a big variety of metal combinations exist that no previously known method of separation is universally operable under standard conditions. The

method of the present invention is insofar unique as by,

proper choice of the complexing agent all metal combinations can be separated at least partially. In adapting the complexing agent to the specific metal combination to .be concentrated and separated, the complexing base is so chosen that it forms complexes with at least one of the metals present. Preferably, however, the complexing base forms complexes with as many of the metals of the combination as possible. The best primary complexing base is the one giving the biggest diiferences in complex stability with the metals in question. If the use of a secondary complexing agent is considered, the primary complexing agent is so chosen as to give complexes with as many as possible of the metals present and the secondary complexing agent is so chosen as to give more stable complexes with as few metals as possible. The complex stability constants governing the extent of complexation are listed comprehensively in Special Publications, Nos. 6 and 7, The Chemical Society, London, cited above. Stability constant values of 1 to 10 are an essential condition for the usefulness of a given complexing agent metal combination.

Furthermore, the complexing has to be rapid. The formation and decay of the complexes taking part in the equilibria have to have a velocity which equals or, preferably, surpasses the scalar value of the effective travel velocity of the ions in the electrical field used. In practice, up to of the value of the concentrations corresponding to the equilibrium should be obtained within a few seconds, preferably within two seconds. If the equilibria of the particles taking part in the process of separation and concentration according to the present invention reach 90% of their final value within 0.5 to 2 seconds, small field strengths of 5 to 20 volts per centimetre are used preferably. If the equilibria are established faster than mentioned above, higher field strengths may be used. Complex formations which have been investigated using glass electrodes whereby stable potential values were reached within a few seconds are useful for the processes according to the present invention without further investigation. The velocity of the complexing can also be judged by rapid end point establishment in complexometric metal titrations. If nothing is known with respect to these criteria when using a new complexing agent, a few trial runs in the analytical apparatus shown in FIG. 1 will establish its usefulness.

By appropriate choice of the concentration of the complexing base in the cathode compartment and the concentration of the complex destroyer in the anode compartment, it is possible to form practically any concentration gradient in the electrode interspace dictated by the specific metal combination to be separated. The numerical values of the concentration gradients with respect to the complexing bases can be 10* up to 1 mol per litre per centimetre using linear interpolation. Values of 10" up to 0.5 mole per litre per centimetre are preferred. The mode of production of the concentration gradient is completely unimportant. It could be produced, for example, by providing adjacent sections of the electrode interspace with constantly diminishing concentrations of complexing base by mechanical means. Much preferred, due to its simplicity, is, however, the electrical production of the concentration gradient as explained above.

Important external characteristics of the concentration and separation method according to the present invention are the temperature, the cooling, the electrode material and electrode distance and the potential applied to the electrodes among others.

The field strength can be 5 to 1000 volts/cm. An upper limit of 200 v./om. is preferred because very high field intensities can cause some operational difficulties. The field intensity has a marked influence upon the concentration and separation of the metals. Small field intensities produce a small concentration gradient which produces excellent separations, but only fairly good concentrations. High field intensities on the other hand, produce a steep concentration gradient with respect to the complexing base capable of excellent concentrations but not preferred for separations.

The electrodes can consist of one of the inert materials usually used. The anode is preferably made from platinum. The cathode is also made from platinum; graphite, nickel, stainless steel can also be used in particular if the apparatus is not of the continuous type which can be in service for a long time. Depending on the use to which the apparatus is put, electrode distances of 2 to 200 cm. are possible, this distance: however, is

not a critical parameter provided that the electrical insulation is done properly.

The temperature at which the process can be run depends on the boiling and melting points of the dielectric used. Temperatures of 10200 C. have been shown to be favourable, a range of 30-100 C. being preferred. High temperatures of, for example, 95 C. offer a great advantage because the heat produced during the process can be dissipated very easily by the use of tap water or brine. Since the viscosity of the usual dielectrics used is very small at such high temperatures, an especially good restriction of the free convection of the solutions in the electrode interspace has to be provided for.

The dissipation of the heat created during the process is essential for the success of the process. The means by which this heat is dissipated is immaterial as such. In any case, however, metal surfaces of cooling aggregates should be prevented from contact with the liquid of the anode compartment, cathode compartment and the electrode interspace because otherwise the electrical field can become ineffective for the separation. All metal surfaces therefore, which are possibly used for the cooling should be insulated very carefully by coating with enamel or glass or a Water resistant plastic layer. One specific example of such a cooling system is shown in FIGS. 6-11.

A good means of dissipating the heat is the evaporation and recondensation of the solvent. In this case great care must be exercised in returning the solvent to the exact place of the electrode interspace from which it was evaporated. Otherwise very unfavourable concentration changes within the concentration gradient may occur.

Another means favourably used is the use of a liquid immiscible with the dielectric used for the separation. This immiscible liquid coolant can serve as a stationary heat reservoir such as is shown in the analytical apparatus in FIG. 1. Another possibility is to mechanically disperse the immiscible liquid coolant in the dielectric, said coolant having a lower boiling point than the dielectric and being evaporated during the process. In this case, the return of the coolant to its original place is not as critical as the return of evaporated dielectric itself.

The geometrical form of the electrode interspace is immaterial as such. In practice, however, it is preferred to give it a form as simple as possible. Thin parallelepipeds are most convenient since they allow efiicient dis sipation of the heat due to the great surface. The electrode interspace has by no means to be filled uniformly with the ion permeable structures which prevent free convection as is the case with the filter paper strip 7 of FIG. 1. Since it is only necessary to prevent free convection in the direction of the electrical field, channel systems with the openings perpendicular to the direction of the electrical field serve the purpose well and allow construction of apparatuses capable of performing separations of large volumes of metal solutions. It is even possible to have the metal solutions flow in a controlled manner perpendicular to the electrical field. FIG. shows the phenomena observed in such a case, when a sheet of filter paper 78 is used as the ion permeable structure of the electrode interspace. Section (a) represents the part of the filter paper sheet which is in connection with the anode compaltment and corresponds to section (a of FIGS. 2 and 3. Sections (11) and (d) have the same meaning as in FIGURES 2 and 3. Section (e) represents that part of filter paper sheet 78 which is in connection with the cathode compartment and corresponds to section (2) of FIGS. 2 and 3. Section (c) represents the electrode interspace through which the solution of the metals to be separated flows in the direction of the arrow A1. When entering the electrode interspace (c), the two kinds, for example, of metal ions are evenly distributed throughout the solution. While flowing through the electrode interspace perpendicular to the electrical field,

which is represented by the arrows Ae, the metal ions are successively focussedby said field. After complete passage through the electrode interspace all metal-carrying particles of one metal leave the electrode interspace in the narrow streaming band designated by h corresponding to the focus f of FIG. 3 and all metal-carrying particles of the other metal leave in the streaming band f corresponding to focus f of FIG. 3.

Again, as indicated earlier, the electrode interspace need not be uniformly filled with ion permeable structures.

E pecially in the case of this continuous concentration and separation apparatus, constructions with canal systems are much preferred. The canals are so built that the liquid fiows exactly perpendicular to the electrical field through them. The flow of said liquors is preferably laminar. The flow velocity is related to the length of the canal. The time obtained when dividing length of canal by flow velocity has to be in the range of 10 seconds to 30 minutes, one minute to 10 minutes being preferred. in any case, the flow velocity is to be so adjusted that complete concentration and/ or separation of the metals is obtained.

It is of prime importance that in all the canals exactly the same flow velocity is maintained. As such it is immaterial whether this condition is arrived at by adjustment of the feed at fixed canal widths or by adjustment of the canal cross-section at fixed feed-rate or by variation of both variables.

Naturally, the canals must have an even cross-section throughout their whole length. The contents of each canal is collected separately on leaving the apparatus, the metals separated and concentrated being isolated direct in the form of their pure solutions.

The total volume of liquor contained in one canal is on the other hand related to the active cooling surface of that canal. The ratio of the two quantities has to be such as to ensure complete dissipation of the heat generated by the electrical current during the operation.

The form in which the metal-containing particles are introduced into the apparatus is an important question in such a continuous process. Chiefly solutions of the metal Salts are used. Of course the pre-formed complexes of the metals with the complexing base used for separation can also be fed into the apparatus in the form of their solutions. A good method is the introduction of a solution in which the metals to be separated are half in the form of their simple metal ions and half in the form of their complexes with the complexing base used in the operation. In the latter case, the concentration of the complexing base in the cathode compartment can be kept at a minimum because the complexing base necessary to complex the metal need not be taken from the concentration gradient. Thus the process gains in economical value.

If a secondary complexing agent is used, the preferred method is to introduce the metals to be separated by it completely in form of the complexes of said secondary complexing agent;

The concentration of the metals in the liquid of the electrode interspace is generally limited by the solubility of the metal salts present in the dielectric used. On occasions super-saturated solutions can be handled when the continuous apparatus is operated carefully. This is the case with metal salts and/or complexes which crystallize slowly. Such substances are prone to stay in supersaturated solution within the apparatus and only crystallize on standing after their solution has been Withdrawn from the apparatus. This is valuable in two respects, because high concentrations mean high throughputs and the metal compounds to be isolated can be obtained, at least partially, by direct crystallization.

A specific construction of a continuous concentration and separation apparatus is given in the specific examples below. The details of this construction are understood 13 to be illustrative only of the invention Without limiting it in any way. Many modifications of such a construction are perfectly obvious to the person skilled in the art.

Some of the diverse technical tasks which the continuous concentration and separation apparatus of the present invention is capable of performing are listed below, without limiting the total capabilities of the method in any way.

(1) The continuous concentration of metals in pure solution using the apparatus described below which is capable of efiiciency factors, i.e. upgrading of concentrations from 1 to up to well over 1 to 100. This upgrading of concentration is of great value in the concentration of radio active metal solutions because no manual work is necessary when the apparatus has once been adjusted to the work to be performed.

(2) The continuous purification and simultaneous concentration of metals through separation of cationic impurities, for example the elimination of alkali metals which are very hard to eliminate by the conventional continuously operating precipitation and filtration methods. In such a case complexing bases are chosen which are useful in the concentration of the metal to be purified but which form either no or only very labile complexes with the alkaline metals, so that the alkaline metals travel into the cathode compartment during the process and the metal to be separated can be Withdrawn from the apparatus in the form of a concentrated pure solution.

Obviously this method is quite general if a metallic impurity has to be removed which impurity forms much weaker complexes with the complexing agent used than the metal to be isolated.

(3) The continuous separation of metal ions from a common solution of said metals as a means of production of solutions of the pure metallic components of said common solution.

It is a special advantage of the process according to the present invention that the geometrical point at which a given metal is collected and can be withdrawn from the apparatus does not depend, within a wide range, on concentration of the feed of the metals, provided that the complexing base gradient is fixed, i.e. the composition of the solution of the complex destroyer in the anode compartment and the composition of the solution of the complexing base in the cathode compartment and the electrical field are kept constant. This is true for the analytical apparatus as well as for the flow apparatus provided that the flow velocity is kept constant in the latter case. Of course at very high concentration of the metal feed solution, the point oi exit can vary slightly. The extreme independence of the point of collection of a metal from the concentration of the metal feed is of great importance as the apparatus need not be adjusted to small variation in concentration encountered in metal mixtures to be separated occurring normally in industrial operations.

This is, of course, of special interest in the separation of radioactive metals. The chemical and physical factors pertaining to a solution of metal salts to be separated can be established, preferably if possible by use of nonradioactive isotopes of said metals. Then the apparatus is adjusted and can henceforth be used without the need of manual maintenance as long as the radioactive solutions are in the apparatus.

As can be seen from the following examples given to illustrate the invention without limiting it in any way, metal ions from all groups of the periodic system of elements can be concentrated and/or separated according to the present invention.

Example 1 The analytical apparatus used for the concentration of metal solutions and for the separations of metals in solu- D successfully be used as the three containers.

tion as described in the following examples is illustrated by FIGS. 1a and lb. FIG. 1a is a longitudinal section and FIG. 1b is a top view, both in natural scale. The apparatus consists of three thin-walled glass containers 1, 4 and 9. The anode compartment 1 contains the anode 3 and the complex destroyer solution 2.

The cathode compartment 4 contains the cathode 6 and the complexing agent solution 5. Both electrodes are made from a rectangular piece of platinum foil to which a platinum wire is annealed, which wire is connected to a convenient source of DC. cunent. The middle container 9 is filled wtih a water immiscible clear liquid 8 serving as coolant. The filter paper strip 7 upon which the separation and/or concentration of the metal ions is carried out, is held in place by holder 1.0. This holder is very simply made from glass rods according to the drawings in FIGS. 1a and 112. A perspective drawing of this holder is given in FIG. 10. Examples of the proper operation of the apparatus are given in the following examples. Although the dimensions of the apparatus are given exactly in FIGS. 1a andlb, and the materials of construction of each component. of the apparatus are specified, this information is only given by way or" an example and should not limit the apparatus in scope. A person skilled in the art should be capable of replacing each material by another one capable of performing the same function and of adapting the dimensions of the apparatus to the intended use. Thus, for instance, the glass holder 11) may be replaced by two ordinary clothes pegs made from plastic, care being taken to avoid too strong a pressure upon the strip as that would squeeze the liquid out of the strip. Ordinary plastic dishes as used in photographic work can very conveniently and Although they do not stand up in service for too long a period of time, the graphite rods found in ordinary flashlight batteries may very well be used as electrodes giving the same result as the more expensive platinum electrodes.

Example 2 The analytical apparatus of Example 1 is used. 50ml. of 0.5 N hydrochloric acid is filled into the anode compartment 1 and serves as complex destroyer solution 2. 50 ml. of a solution which is 0.5 N with respect to sodium hydroxide and 0.2 M with respect to disodium hydrogen nitrilotriacetate is filled into the cathode compartment 4 and serves as complexing agent solution 5. The cooling bath 9 is filled with carbon tetrachloride. Tetrachlorethylene, tetraline, o-dichlorobenzene, xylene, amyl acetate and other inert liquids of this class may as well be used as the carbon tetrachloride.

0.05 ml. of a solution which is 0.005 M with respect to FeCl NiCl ZnSO Al(NO U02(NO3)2, CoCl CrCl and MnSO is spread into the middle part of a filter paper strip 7 (Whatman No. l) which is 2 cm. wide and 18 cm. long. A wet zone of approximately 12 width, corresponding to section (c) of HG. 2 is obtained. Then one end of the strip corresponding to section (a) of FIG. 2 is immersed in the anode liquor and the other end, corresponding to. section (e), is immersed in the cathode liquor. As soon as the two electrode liquors are sucked into the filter paper strip and by capillary action reach the zone wetted by the metal salt solution (thereby filling the parts corresponding to sections (b) and (d) of the filter paper strip with anode and cathode liquor respectively), the strip is immersed in the cooling liquid 8 with the help of glass holder 10. A DC. potential of 200 v. is applied to the electrodes 3 which is the anode and 6 which is the cathode. A current of approximately 10 ma. ensues immediately. Then the current slowly increases to about 20 ma. and remains at this value for 1 to 2 minutes. Then the current decreases to approximately 10 ma. again and remains at this value 15 for a prolonged period of time. After 7 minutes, full separation is reached. Further passage of the current does not alter the visually observed picture. Upon very long passage of the current slight shifts of the coloured.

lines occur due to a minute change of the concentration gradient of the complexing base caused by excess immigration of the fast moving protons from the anode liquor into the electrode interspace. After minutes the strip is removed from the apparatus and dried as quickly as possible with the aid of the hot air stream of a hair dryer. Visual inspection of the strip reveals several coloured stripes approximately 0.5 mm. in width across the strip. From cathode side to anode side there are first a violet line (referred to as focus 2) then at a distance of 2.5 to 3 mm. a pink one (referred to as focus 3), then at a distance of 5.5 mm. from focus 2 a yellowish brown one (referred to as focus 4), then at a distance of 14 mm. from focus 2 a greenish blue one (referred to as focus 7) and lastly at a distance of mm. from focus 2 a brownish line (referred to as focus 8). Four 3 mm. wide strips are then cut lengthwise from the filter paper strip 7. The first of these strips is sprayed with a 1% solution of potassium ferrocyanide in water. Then the strip is immediately dried again with the hair dryer. Focus 4 is now a solid brown and focus 8 a deep blue. During the spraying some smearing over of the foci is observed so that the lines now seen are up to 1 mm. in width. If the spraying and drying are not made carefully the width of the foci can reach values of over 1 mm. and they can also interfere with each other. The second of the small strips is then sprayed with a 1% alcoholic solution of dithio-oxamide. Then the strip is dried as before and is placed over a dish containing concentrated ammonia solution. On the cathode side of focus 2 there now appears a new line, brown in colour and at a distance of 2 to 3 mm. from focus 2. This new line is referred to as focus 1. Focus 7 now appears as a violet line, focus 8 as a black line and focus 3 as a brownish line. The third of the small strips is sprayed with a 1% solution of dithizone in alcohol. Then the strip is dried with the hair dryer and placed over concentrated ammonia solution as before. Again focus 1 presents itself as a brown line. Between foci 4 and 7 there appears a new red line at a distance of 9 mm. from focus 2. This new line is referred to as focus 6. The fourth of the four small strips is spread wtih a 1% solution of Morine in alcohol. Then the strip is dried as before. Focus 8' now appears dark brown. When the strip is inspected under a UV lamp there is seen an intensely fluorescent line occurring between foci 4 and 6. This new line which lies at a distance of 7 to 8 mm. from focus 2 is referred to as focus 5. From the above spot tests and the visual inspection of the original dry strip, it is concluded that the metal ions originally present in the metal solution have been separated completely from each other and that in focus 1 (i.e. the one occurring nearest to the cathode) all the manganese is accumulated (oxidation of the manganous hydroxide formed under the influence of the ammonia vapours to the brown manganese dioxide), whereas in focus 2 all the chromium is concentrated, in focus 3 all the cobalt, in focus 4 all the uranyl, in focus 5 all the aluminium, in focus 6 all the zinc, in focus 7 all the nickel and in focus 8 all the iron. From the above cited Special Publications, logarithms of the stability constants of the complexes of the metals used with nitrilotriacetic acid as complexing agent are read as follows: Mn 7.44, Co 10.38, Zn 1067, Ni. 11.53, Fe 15.87. The stability constants of Cr, U0 and A1 are not given. It is seen from the constants published that the metals are focussed in the order of their stability constants. The metals of lowest stability constant occur nearest to the cathode, i.e. at high complexing base concentration. The metals of highest stability constant occur nearest to the anode, i.e. at high complex destroyer concentration.

Then the remaining part of the filter paper strip 7 is cut up transversely and the separate pieces are extracted With 1 N-hydrochloric acid. Solutions of the pure metals originally present in the mixture are thus obtained. If the accurate location of the metals has once been determined, strip 7 is directly cut up into the segments containing the separate metals for the purpose of quantitative isolation of the metals provided the separation has been carried out in exactly the same manner as the original separation used for the location of the metals.

The same result as above is obtained when the concentration of the individual metal salts in the common solution is 0.002 M or 0.01 M. A change of the anions contained in the metal salts does not influence the results obtained above provided said anions do not form insoluble precipitations with one or more of the metals present and that they are derived from strong mineral acids such as sulphuric acid, nitric acid, hydrochloric acid or hydrobromic acid. For the first reason phosphate anions are not suitable. The same results as above are obtained when a potential of 500 v. is applied to the electrodes with the exception that the current rises to approximately 40 ma. and the foci are formed more quickly, i.e. within 2 to 3 minutes.

Example 3 0.05 M solutions of the salts of the following table are spread near the middle part of the filter paper strip 7 as used in Example 2 so as to form a wet zone of 25 mm. width. Approximately 0.1 ml. solution is needed to do this. 50 ml. of complexing agent solution of the composition indicated in column 3 of the following table are filled into the cathode compartment of the analytical apparatus used in Example 2. 50 ml. of complex destroyer solution of the composition indicated in column 4.. of the following table are filled into the anode compartment. The ends of the strip are immersed in the electrode liquors and the strip is immersed in the cooling liquid in exactly the same manner as described in Example 2. A potential of 500 v. is then applied to the electrodes for 10 minutes. The filter paper strip is then removed from the apparatus and dried as in Example 2. The width of the foci obtained is measured directly in the case of coloured metals. In the case of uncoloured or slightly coloured metals, the focus is rendered visible by the method indicated in column 6 of the following table. Since in every case pure metal salt solutions are concentrated in this example the method of visualization need not be a characteristic reaction of the metal ion as is the case in separations. The specific and characteristic identification of metals is most conveniently made by use of spot tests according to Fritz Feigl, Spot Tests,

vol. 1, 4th edition, Elsevier Publishing Co., 1954.

Due to the unavoidable smearing and broadening of the foci during the various spraying and drying operations needed in the identification of the location of the foci, no accurately reproducable measurement can be made. The maximum width of the foci after the visualization processes are therefore given in two classes only Class 1 represents foci of 1 mm. in width or less. This corresponds to an increase of the concentration of the metal solution of 1:25 or better. Class 2 represents foci of 1 to 5 mm. in width. This represents a concentration efliciency of 1:5 up to 1:25.

In the following table NTA stands for the triply charged anion of nitrilotriacetic acid, UDA stands for the doubly charged anion of uramil diacetic acid, Whereas the quadruply charged anions of the following acids are characterized by the symbols set in brackets: ethylene diamine tetra-acetic acid (EDTA), cyclohexane-1.2-diamine tetra-acetic acid (CDTA), fi.fi'-diaminoethylether tetra-acetic acid (ME) and ethylene glycol-bis-(fi-aminoethyl)-ether tetra-acetic acid (DE).

metal ion and salt of metal used complexing agent complex destroyer focus of mode of visualization Al (III):

chloride 0 5 N 1 spraying with a 1% alcoholic acetate--. 0 5 N 1 solution of Morine. Fluosulphate-.. 0 5 N 1 resccnce under UV lamp of NaAlEDTA 0 8 N 1 Ex. 2. Ag

nitrate 0.5 N 2 sulphate. 0.5 N 2 Has (0) black. nitrate" HiME (b) 0.5 N 2 As (III):

cllgori 11.6 N H01 l N H 1 H28 (0) yellow. chlonde- 'HSNTA (d) 1 spraying with a 0.2% aqueous nitrate HiEDTA (b) M 5 1 solution of Na-rhodizonate. acetate HiCDTA (b) 0.5 N 1 Slamsspralyi g 1:1 li% alcoholic so u 1on0 y roxyquinoiilTfi Sidliiib. i lineggg ag K215801115 3. e OWlS chloiide HiDE (b).. 0 5 N H01 1 fluorescence under UV Cd (II): V \I O1 lampsulphate Hal TA (0) 1 l H 1 chloride H4ED TA (a) 1 N H01 1 1jflls 00 (In: 11 SNHCI 1 acetic acid a: 1 Pink chloride chloride Li (I):

chloride lactic acid (e) chloroac'etic acid oxalic acid (e) malonic acid (2) succinic acid ((2)-- a-hydroxyisobuiyricacid 2e): tartaric acid (I carbonic acid (h) pyropbosplioric acid (5) thiocyano acid 11.6 N H01 acetic acid (e) chloracetic acid (e)- oxalic acid (f) malonic acid (e).

zgzzzz zz succinic acid (e)- lactic acid (e) tartaric acid (I).. citric acid (f) salicylic acid (I) carbonic acid (h) HSNTA (c) HiEDTA (a) a-hydroxyisobutyric acid (e). pyrophosphoric acid (e) thiocyanic acid (q) glycine (e) 11.6 N H01 acetic acid (e)- oxalic acid (2).. chloracetic acid lactic acid (e)c- H4ME (a) thiocyanic acid (2)... pyrocatechol disulphonic acid (k). 2.3-dihydroxynaphthalene- 6-sulph0nic acid (Z).

H EDTA (a) N4lVIE (a) HsNTA (c) II DE v4 ((l H EDTA (a) H4ODTA (a) HiE D TA (a) lactic acid (1:) a-hydroxyisobutyric acid (a). HaNTA (c) HiME (a).. H CDIA (a) 2 N N503 2 N HNOs 2 N HNOa 2 N BNO: 2 N HNO:

2 N HNOa 2 N H01 1 N Roi;

1 N HNOa H2UDA (0) lNHOl visible pink.

visible greenish.

visible blue.

visible blue.

visible yellowish brown.

}Mor inc-same as aluminium. }H2S (a) black.

}Moriuesame as aluminium.

sprayed with a 0.2% alcoholic solution of Quinalizarine. Development with gaseous NH; blue.

ace-2,597

metal ion and salt of metal used complexing agent complex destroyer 033118 of mode of visualization c ass Mg (II):

sulphate HBNTA (d) 1 chloride. HiODTA (b) 1 same as Ca. gives more N a MgEDTA H EDTA (b) 1 greenish fluorescence. chloride HiME (b) 1 Mn t acetic acid (e) 1 sprayed with aqueous 3 H NTA (d) 1 NHa solution and developgulgiiate' I HiDE @0111: 1 ff Q lf 3 chloride Elnora (a) 1 5 y Mo (V I):

(NHmMoOi carbonic acid (/2) 0.5 N HNO3 K-xanthate (g). Na (1):

chl)0ride HzUDA (y) 0.5 N H01 flame (p).

' oxalic acid (m). 2 M HzSOi radioactive N b (r).

visible greenish-blue.

}-H2S (0) black.

oxalic acid (in) lactic acid (e) HQNTA (c)( H 8 (0) orange.

}Quinalizarinesame as La.

HQNTA (d) HQNTA (d) menu 11 H ME (by His (0) brown.

}Na rhodionate-same as Ba.

l l l 1 visible (yellow-orange).

l l l 1 oxalic acid (m) 2 N Has 04 radioactive Ta. (r). lactic acid (6) 1 11:; 1 L

1 4 uinalizarine-same as a.

H4EDTA {0. 2 M rumor). 1 Q

oxalic acid (m) 2 N H2804 2 radioactive Tl1 (r) oxalic acid (m) 2 N H2804 2 H202 (s). HiEDTA (b) 0.5 N HNOs 1 flame (p).

a hydroxyisobutyric acid 1 N H01 1 e Quinalizarinesame as La. HiME (a) 1 NHCl 1 acetic acid (.2) Q 0. 5 N H01 l tartaric acid (I) 1 HiEDTA 2 visible yellowish-brown. HiNTA (d) 1 carbonic acid (It) 0. 5 N H01 1 tartaric acid (I) 1 N H01 1 HaNTA (d) 1 N 1101 1 }V1S1b1e bluelactic acid (e) 0 1 a-liydroxyisobutyric acid (6). 1 HaNTA 1 Quinallzarine-same as La. HiEDTA (a) 1 HiEDTA (a) 1 11.6 N 1101 1 iifi ii ii gzffij Dithizone (see Example 2). H4ME. 1

oxalic acid (in) 1 ZrO(NO )g oxalic acid (m) 1 }mdlactlve F The letters used in the above table have the following (d) represents a 0.1 M solution of the disodium hydrogen meaning; salt of the acid specified, which solution is also 0.1 N

with respect to sodium hydroxide.

( represents M Solution of ihe dISOdlllm y (e) represents a solution prepared as follows: 0.5 g. M01 gen salt of the acid spe ifi d in c l m 3- I of the acid specified in column 3 are dissolved or slurrepresents a M Sohlficn of the disodium y ried in approximately 800 ml. of Water and the mixture gen salt of the acid pe which solution is also 0- is neutralized with 5 N sodium hydroxide solution to a N With respect F Q Y X B. Such a solution pH of 6.3 and then diluted to exactly 1 litre. If no 18 made P Y dlssolvlng 8- Mol of the disodium pH-meter and glass electrode is available, the neuhydrogell Salt-ill 500 of N Sodium hydroxide tr aliz ation can be made if methyl red is used as indi- SOilltiOIl and diluting the resulting solution 110 0116 litre. atar and odium hydroxide solution is added until an A solution of exactly the same composition is obtained orange colour i b i d, when 0.1 g. Mol of the free tetra-acetic acid specified is (f) represents a l ti d as under i h th dissolved Wlllh a Solution f M01 f i m ception that 0.1 g. Moi of the acid specified is used. droxide in approximately 800 ml. of Water and the r (g) represents a solution which is 0.05 M with respect tosulting solution is then diluted to exactly one litre. V dipotassium uramil diacetieacid and 0.2 N with respect (0) represents a 0.1 M solution of the disodium hydrogen potassium hydroxide.

salt of the acid specified in column 3. V (h) represents a 0.1 M solution of ammonium carbonate.

(i) represents a 0.1 M solution of ammonium thiocyanate.

(k) represents a 0.05 M solution of the disodium pyrocatechol disulphonate.

(1) represents a 0.05 M solution of the sodium 2.3dihy droxynaphthalene-6-sulphonate.

(m) represents a saturated solution of oxalic acid dihydrate.

(n) The solution of the ruthenate is prepared as follows: 1 part of ruthenium metal is mixed with 3 parts of KCl and 9 parts of NaOH. The mixture is heated until the mass is molten throughout whereupon the ruthenium dissolves instantaneously. The melt is cooled and leached with water. The aqueous solution is diluted to be 0.05 M with respect to Na RuO (0) The strip is sprayed with a saturated aqueous solu' tion of H S and dried.

(P) The strip is cut up transversely into pieces of 0.5 mm. width and the individual pieces are burned on a platinum wire. Only the one or two (depending upon the incidental relation of cut and focus) pieces of the filter paper strip in which all the metal is concentrated give the characteristic flame colouration of Li, Na or T1.

(q) The strip is sprayed with a freshly prepared 2% aqueous solution of potassium ethyl xanthate and the pink colour is developed with gaseous H61.

(2') The metal solution is provided with a tracer amount of the radioactive isotope indicated in column 6 of the above table (10 microcuries/ ml. of solution) and the location of the focus is determined as described in Example 4.

(s) The strip is sprayed with a 3% aqueous solution of hydrogen peroxide to yield a yellow-orange focus.

Example 4 50 ml. of a solution which is 1 N with respect to perchloric acid and 0.1 M with respect to ferric perchlorate is filled into the anode compartment and 50 ml. of a 0.3 M solution of disodinm dihydrogen ethylene diamine tetraacetic acid is filled into the cathode compartment of the same apparatus as in the above examples. A solution which is 0.04 M with respect to PrOl NdCl CeCl and La-Cl each of which metal salt contains a tracer amount of radioactive isotopes, is spread on the filter paper strip so as to produce a vet zone of 25 mrn. in width. The following isotopes are used as tracers:

*"Nd: (half life 11.6 days),

th: (half life 17 minutes), cc: (half life 285 days) ica: (half life 40.2 hours),

each in an amount of 10 microcuries per ml. of solution.

Then the strip is immersed in the electrode liquors and the cooling bath as in the previous examples. Then a potential of 500 v. is applied to the electrodes for 10 minutes. The strip is removed from the apparatus and dried as described above. The dry strip is put between two cellophane strips of the same dimensions and a thickness of 2 mg./cm. With the aid of a motor, the strip is then moved, beginning with the cathode end of the strip, at a velocity of 2.8 min/min. under a Geiger-Muller counter tube (Philips EZ No. 18,505) which is shielded by a 2 cm. lead shield. A 2 mm. thick brass shield is put in between strip and counter tube, which brass shield has a slit of the dimensions 0.5 mm. X 20 mm. and is so oriented that the slit is perpendicular to the length axis of the filter paper strip and hence parallel to the feel on the strip.

Complete passage of the filter paper strip under the counter tube reveals 4 bands of radiation, the intensity of which is determined by the counts given by the counter tube. The distance of the bands from each other is 3i0.5 mm. and they are referred to as foci 1 to 4 beginning with the one nearest to the cathode. After minutes the strip is run under the counter tube in the same Way as above. Focus 3 shows a marked reduction of the count by almost half of its original value. Focus 2 shows an increase of the count by the same amount that focus 3 dropped. Foci 1 and 4 produce the same number of disintegrations per minute as originally. Focus 3 therefore contains all the Pr originally present in the solution and focus 2 all the Ce. The increase in the activity of the Ce focus is due to the formation of the short lived daughter element *Pr upon emission of the fi-rays. After two days the strip is measured again as above. The activity of focus 3 is nearly all gone, focus 2 has increased in activity by the amount originally present in focus 3, focus 1 has dropped in activity by about half and focus 4 remains practically constant. Focus 1 is thus identified as the band containing all the La originally present. After 14 days another count is taken. Focus 3 gives practically no counts any more, focus 2 remains constant compared to the third measurement, focus 1 shows a very small fraction of the original counts and focus 4 produces about one half of the original disintegrations per minute. Focus 4 is thus identified as the band containing all the Nd originally present in the common solution.

The logarithms of the stability constants of ethylene diamine tetra-acetic acid with the metals used is given in the Special Publications cited above as La (focus 1): 15.50, Ce (focus 2): 15.98, Pr (focus 3): 16.40, and Nd (focus 4): 16.61. Again the metal forming the least stable complex is found nearest to the cathode and the metal giving the most stable complex is nearest to the anode.

Example 5 In the same apparatus as used in the previous examples, 1 N hydrochloric acid containing 0.5 g./lit-re of a non-ionic wetting agent (Tinovetin NR of Geigy) is filled into the anode compartment and 11.6 N HCl again containing 0.5 g./litre of the same wetting agent is filled into the cathode compartment. A solution which is 0.05 M With respect to FeCl AsCl CoCl and CuCl and containing 0.5 lg./litre of the same wetting agent as above, is applied to a strip of polyvinyl chloride fabric cut in the dimensions of 2 x 18 cm. from an ordinary polyvinyl chloride filter cloth so as to form a wet zone of 25 mm. in width. Approximately 0.08 ml. of solution is needed to do this. Then one end of the strip is 'immersed in the cathode'liquor and the other end in the anode liquor. After penetration of the electrode liquors to the zone wetted by the metal solution, the strip is cooled with the cold airstream of a non-heated hair drier and a potential of v. is applied to the electrodes. After 10 minutes, the current is interrupted and the hair drier is changed to deliver hot air and the strip is thus dried. Three bands are identified by direct visual inspection, a brown yellow iron focus, a greenish copper focus and a bluish-red cobalt focus. The focus containing all the arsenic is made visible by spraying the filter paper strip with a saturated aqueous solution of H 8. This treatment produces a black copper focus and a yellow arsenic focus.

Example 6 In the same apparatus as used in the previous examples, 0.5 N hydrochloric acid is filled into the anode compartment and a solution which is 5 M with respect to sodium acetate and 5 N with respect to acetic acid is filled into the cathode compartment. A solution of 0.01 M with respect to UO (NO FeCl Cr(III) acetate and C080,; is applied to the filter paper strip so as to produce a wet Zone of 40 mm. in width. Approximately 0.16 ml. of solution is needed to do this. The ends of the strip are immersed in the electrode liquors and the strip is immersed in the carbon tetrachloride, as described in Example 2. A potential of 500 v. is applied to the electrodes for 5 minutes. Then the strip is dried as in Example 2. Four bands are detected upon visual inspection at a distance of 1 mm. from each other. Next to the cathode the cobalt focus is found, then the chromium Into the same apparatus as used in the previous examples, 0.5 N nitric acid is filled into the anode cornpartment and a 0.1 M solution of disodium calcium ethylene diamine tetra-acetate is filled into the cathode compartment. A solution which is 0.05 M with respect to disodium mercury ethylene diamine tetra-acetate, disodium copper ethylene diamine tetra-acetate, disodium lead ethylene diamine tetra-acetate and disodium cadmium ethylene diamine tetra-acetate is applied to the filter paper strip so that a wet zone of 25 mm. width is obtained. Proceeding exactly as described in Example 2,

four foci are obtained in the following sequence: Cd

focus nearest to the cathode, at 2 mm. from it the Pb focus, 1 mm. from the latter the Cu focus and 1 mm. from the Cu focus the Hg focus nearest to the anode. Of these only the copper focus is observed direct. The mercury focus is visualised with Dithizone as a red band by spraying the strip with Dithizone solution and developing it as in Example 2. T he Hg, Pb and Cu foci are rendered black by the action of gaseous hydrogen sulphide upon the slightly moist strip, whereas the Cd focus is transformed into a pure yellow line.

Again the metal forming the most stable complex is found nearest to the anode (Hg log K 21.80) and the one forming the least stable complex nearest to the cathode (Cd log K 16.46), the others lying inbetween in order of their stability (Rb log K 18.04 next to Cd; on log K 18.80 next to Hg).

Example 8 Proceeding as described in Example 2, CuCl NiSO and CoClwhen present originally in a common solution are separated if 0.1 M ferric chloride solution (50 ml.) is filled into the anode compartment and 0.1 M disodium calcium ethylene diamine tetraacetate solution (50 ml.) is filled into the cathode compartment. Application of a potential of 500 v. and working as described in Example 2 produces three coloured foci at a distance of 2 from each other. The cobalt focus lies next to the cathode, the Cu focus next to the anode and the Ni focus inbetween.

Example 9 In the same apparatus used in the previous examples, a solution of 0.2 M with respect to diammonium dihydrogen ethylene diamine tetra-acetate, 2 M with respect to sodium acetate and 2 M with respect to acetic acid is filled into the cathode compartment and 0.5 M hydrochloric acid is filled into the anode compartment. CoCl NiSO and CuSO each in a concentration of 0.01 M in a common solution are applied to the strip. Application of a potential of 500 v. proceeding otherwise exactly as described in Example 2 produces 3 foci, Co(lI) lying next to the cathode, 3 mm. from it the Ni(ll) and 5 mm. from the latter the Cu(Il) next to the anode.

Example In the same apparatus as in the previous examples, 0.3 M diammonium hydrogen nitrilotriacetate solution is filled into the cathode compartment. A solution 0.25 N with respect to HQ and 11.25 N with respect to HP is filled into the anode compartment. A solution 0.01 M with respect to Tb(lll), Yflll), La(lll) and Sr(ll), each metal in form of its chloride and containing a tracer amount of radioactive isotope (10 microcuries/ml. of final solution), is separated into its components by application of 500 v. to the electrode and the same procedure as described in Example 4. Identification of the foci analogously to Example 4 reveals the Sr focus nearest to the cathode, 10 mm. from it the La focus, 10 mm.

Car

24 from the latter the Y focus and 6 mm. for the Y, the Tb focus.

Exactly the same procedure produces 3 foci from a mixture of Tmflil), Y(llI), and Sr(II), each originally present in the form of the chloride. The Sr focus is found next to the cathode, 20 mm. therefrom is the Y focus and 8 mm. from the latter is the Tm focus next to the anode.

Example 11 in the analytical apparatus used in the above Examples 2, 3 and 4, l N hydrochloric acid is filled into the anode compartment and a solution which is 1.2 M with respect to sodium acetate and 0.4 N with respect to acetic acid is filled into the cathode compartment. A solution which is 0.1 M with respect to ferric perchlorate and cobalteous perchlorate is applied to the filter paper strip so as to form a Wet zone of 25 mm. in width. Immersion of the filter paper strip in the electrode liquors and the cooling liquor (carbon tetrachloride) is done exactly as described in Example 2. Then a potential of 500 V. DC. current is applied for 7 minutes which produces two sharp foci which, however, lie very close together (approximately 1 mm. distance). If a solution which is 0.03 M with respect to disodium hydrogen nitrilotriacetate and contains the two metals in the same concentration as above is applied to the strip as described above and the focussing is carried out exactly as described above, then three coloured bands appear, two yellowish brown and one pink. Spraying the strip with a 1% aqueous solution of potassium ferrocyanide as described in Example 2 reveals two iron foci, one of which is located at the same place as the iron focus if no nitrilotriacetic acid is added to the metal solution. The other iron focus appears much 1 carer to the anode. The second experiment is repeated and the strip is cut up transversely so that the two small parts of the strip in which the two iron foci are located are isolated from the rest of the strip. The two little strips are then ashed in platinum crucibles with the aid of fuming nitric acid and a few drops of concentrated sulphuric acid until all organic material is destroyed and a residue free of carbonous matter is obtained. The amount of iron is then determined spectrophotometrically with the aid of dithio-oxamide. The amount of iron found in the newly formed focus near the anode side of the strip amounts to 30:5% of the total amount of iron present on the strip and hence is Within the limit of error of the experiment equivalent to the amount of nitrilotriacetic acid present. This is further verified by the following experiment. A solution which is 0.1 M with respect to disodium hydrogen nitrilotriacetate, ferric perchlorate and cobaltous perchlorate is applied to the strip and the focussing is executed in the same Way as described in the first of these three experiments. Only two foci are produced, namely the cobalt focus in its original place and the one iron focus in the place near the anode side of the strip. This phenomenon is referred to in the following examples as complete double focussing.

If the concentrations of the above three components of the metal-containing solution applied to the strip are reduced to one one-tenth of the concentration given above (i.e. to 0.01 M) exactly the same results are obtained.

If however, the concentration of the metals is reduced to 0.0001 M, a concentration of 0.0002 M disodium hydrogen nitn'lotriacetate is needed to produce only two foci. At this low concentration a complete double focus- Sing, therefore, no longer occurs. The need of a more than equivalent amount of secondary complexing agent over the metal which is double focussed will be referred to as incomplete double focussing.

which is 0.05 M with respect to Feflll), copperfll) and lead(ll) all in form of their perchlorates, is applied to act-2,597

25 the filter paper strip. Anode and cathode liquors are the same as in Example 11.

The focussing as described in Example 11 provides three metal bands lying close together. If now, an increasing quantity of the disodium salt of ethylene diamine-tetra-acetic acid is added to the metal solution applied to the filter paper strip, the following phenomena successively take place:

After focussing, a part of the iron first appears in a new focus nearer to the anode, while the three original bands remain but the original iron band decreases in intensity. When a quantity of ethylene diamine tetra-acetic acid exactly equivalent to the quantity of iron present is reached, again just three sharp metal bands appear, the iron band being pushed strongly towards the anode as compared with the copper and lead bands. A further increase in the amount of ethylene diamine tetra-acetic acid causes the appearance of four bands again, the iron band being situated nearest to the anode, closely followed by a copper focus, and at a further interval is another copper focus and the lead focus. If the amount of secondary complexing agent added rises to an amount which corresponds to the sum of the iron and copper, there are again only three bands, i.e. the iron band near the anode, close beside it the copper band, and at a further interval therefrom, the lead band. Further increase of the ethylene diamine tetra-acetic acid causes the renewed appearance of four bands, i.e. an iron focus, closely followed by a copper focus, closely followed by a lead focus and at a further distance therefrom, a second lead. focus. If the amount of ethylene diamine tetra-acetic acid is equivalent to the sum of the three metals present, there are again only three bands which now all lie close to the anode. A further increase in the content of the secondary complexing agent no longer alters the picture.

Example 13 Following the procedure described in Examples 11 and 12 and using the same anode and cathode liquors and using concentrations of 0.1 M with respect to the metals listed below, which are used in the form of their perchlorates, the secondary complexing bases below have the following elfect on the focussing.

The same results re obtained if a solution which is 2.5 M with respect to sodium acetate and 0.5 M With respect to acetic acid is used as cathode liquor. The same results are also obtained if the concentration of the metal salts is 0.01 M. The same results are obtained if Co(II) sulphate is used instead of the perchlorate; also if nickel chloride is used instead of the perchlorate; also if lead acetate is used instead of the perchlorate; also if the nitrates of the metals listed are used instead of the perchlorates. However, if lead is present, no other metal should be used in the form of its chloride or sulphate since this hinders the separation.

A continuous type of apparatus capable of functioning for a long time is shown in FIGS. 6-11.

The main part of the apparatus is a separation chamber formed by two glass plates and 14 filter paper strips subdividing the space between the two glass plates. This separation chamber is placed between and made watertight with two rubber washers against a base plate and a top plate providing the mechanical support. The separation chamber is provided with a cooling system and a feeding system. The pure metal solutions are collected from the separation chamber by means of a withdrawal system.

FIG. 6 is a top view of the base plate 11 with the central portion omitted and FIG. 7 is a sectional view of the top plate 12. FIG. 8 is a cross section through the separation chamber. Two rubber washers 18 and 19 and base and top plates 11 and 12 have cooling tray walls 20 and spray protection walls 21 fastened thereto respectively. These five elements are shown separated to indicate how they are fitted together.

Base plate 11 is made from polymethyl methacrylate having the dimensions 34.5 cm. x 9.5 cm. x 1.1 cm. A central rectangular opening 11a is cut out of the center of the plate so that a rectangular frame is produced. Two side grooves 111) are formed to a depth as shown in FIG. 8 and having a length of 32.5 cm. The grooves 1101-11013 and 11d1-11d13 as well as the slots g and [1 are cut to the same depth as the side grooves 112) and with the shape shown in FIG. 6. Then the rectangular frame Me is cut to the depth shown in FIG. 8 and the screw holes 111 are bored out.

The top plate 12 shown in FIG. 7 is made from polymethyl methacrylate with a length of 34.5 cm. The areas 12a, 12b, 12cli-12c13, 12d112d13, and 12 on top plate 12 are cut out completely.

The actual separation chamber consists of two identical glass plates 13, and 14 filter paper strips 14 having a thickness such that they will fit into the slots g and h of base plate 11 and cut to a width such that they will fit in between the two glass plates 13 as shown in FIG. 8. These filter paper strips and the two glass plates form 13 canals 15. FIG. 9 shows the lower glass plate 13 and the filter paper strips 14- and the two electrodes 16 and 17. When placed over FIG. 6, FIG. 9 shows how the glass plate, the filter paper strips and the electrodes are positioned with respect to the base plate 11. To assemble the parts of the apparatus there is introduced into area 11c of base plate 11 a washer 18 cut from soft rubber and having the dimensions of this area 11c. Then the lower of the two glass plates 13 is placed into this area lle so that hole 11a is covered and the upper surface of the glass plate is at the same level as the depth to which the areas 111:, 11c1-11c13, 11d1-11d13 and 11g and h are cut into the base plate. Then the 14 filter paper strips 14 are laid exactly parallel to the longer sides of the frame and the ends are fitted into the slots 11g and h. The second glass plate 13 is then laid on top of the strips as shown in FIG. 8. The upper surface of this upper glass plate has to be at the same level as the upper surface of the base plate 11.

A second rubber washer 19 cut to the same form as top plate 12 from soft rubber is then placed on the upper glass plate 13 and finally the top plate is placed on top. The two plates 11 and 12 in between which the separation chamber lies are, then screwed together by screws (not shown) through the holes This assembly will be referred to as separation unit. I

The separation unit is then placed in an absolutely horizontal position and held by clamps attached to stands. Then four walls of a cooling tray 20 made from polymethyl methacrylate are glued to the upper surface of the separation unit with monomeric methyl methacrylate containing approximately 1% of benzoyl peroxide which is allowed to polymerise overnight. Four walls forming a spray protection chamber 21 made of the same material are attached to the lower surface of the separation unit in the same way. FIG. 8 shows the position of the longitudinal walls and the end walls are attached to the ends act-2,597

of the upper and lower surfaces of the separation unit respectively substantially in alignment with the transverse legs of frame 112. (See also FIG. 11.)

Lengths of copper tubing 22 and 23 in which spray holes have been bored are shown in FIGS. and 11 and are clamped into position in the cooling tray and the spray protection chamber 21, and are connected with running tap water. A rectangular anode 16 made from 0.2 mm. thick platinum sheeting is cut to fit into one hole 12b of the top plate 12. Two platinum rods are annealed to the anode, one of which is connected to the source of DC. current and the other of which serves to keep the anode in position with the help of an insulated clamp. The cathode 17 is made in a similar manner from nickel sheeting and is put into the other hole 12b of the top plate 12 in exactly the same manner as the anode.

The anode compartment 24 located in one hole 12b of top plate 12 is cooled with the help of two pieces of glass tubing 25 of /2 mm. wall thickness and 5 mm. inner diameter, which are held in position with clamps as indicated in FIG.v 10 and connected by rubber tubing to a water tap. The cathode compartment 33 positioned in the other hole 12b of top plate 12 is cooled by identical tubing.

As seen in FIG. 11, the feeding system consist-s of 15 one litre Mariotte flasks 26 containing the feed liquids, the outlets of which are connected by rubber tubing to capillary tubes 27 which are cut from glass tubing 80 cm. long and having 0.4 mm. inner diameter and which are bent as shown in FIG. 11. The ends of the capillary tubes are connected by rubber tubing to glass tubes 29, the ends of thirteen of which are placed 2 to 3 mm. over the feed holes 1201-12c13 of the top plate 12. "The remaining two are placed in the electrode compartments 24 and 33 located in holes 12b of top plate 12. The whole lengths of the capillary tubes 27 are submerged in water held at a constant temperature and contained in a polyvinyl chloride tray 28 with the dimensions of 50 x x 10 cm. The glass tubes 29 from the end of the capillary tubing to the feed holes 120142013 have an inner diameter of 2 mm. and a wall thickness of /2 mm. The withdrawal system consists of 15 individual vacuum sample changers 30 as shown in FIG. 11. Each vacuum sample changer is fitted with one glass tube 31 10 cm. in length and with an inner diameter of 0.7 mm., the end of which is in one of the withdrawal holes l2dll-12d13 of top plate 12, the extra two tubes being connected with the respective electrode compartments. Each vacuum sample changer is also fitted with a vacuum rubber hose which is connected to one of the side arms of a large glass tube which is connected to the aspirator 32. This vacuum distributor is not shown in FIG. 11.

Although the dimensions of the apparatus are given exactly and the materials of each component of the apparatus are specified, this information is only given by way of an example and should not limit the apparatus in scope. A person skilled in the art should be capable of replacing each material by another one capable of performing the same function and of adopting the dimensions of the apparatus to the intended use. Thus, for instance, the glass plates 13 can be replaced by aluminum plates which are insulated by means of a thin porous free layer of polyepoxide resins (Araldite of Ciba Co.). This provides better cooling but does not allow visual inspection of the progress of separation during the flow of the liquids through the separation canals. The use of strips of blown cellulose esters (Porvic) instead of the filter paper strips does not alter the functioning of the apparatus.

Example 14 This is an example illustrating the proper mode of operation of the apparatus described above. It is also representative of an actual continuous separation of copper and cobalt.

Prior to the separation, the cooling system is set in motion by flowing tap water through the perforated copper tubing 22 and 23 and the electrode compartment coolin' systems 25. Excess water accumulating in the cooling tray 20 is run 055 through vtheoutlet 20a which has been inserted in one of the side walls of the cooling tray 20. The water dripping from the spray protection chamber 21 is collected in a vessel connected with a sink.

A solution 2.5 M with respect to sodium acetate and 0.5 M with respect to acetic acid is filled into five of the Mariotte flasks the first one being connected with the cathode compartment, the second with feed hole 1201, the third with feed hole 1202, the fourth with feed hole 1203, and the fifth with feed hole 1204.

A solution being 0.025 M with respect to cobalt nitrate, 0.025 M with respect to copper nitrate, 0.06 M with respect to sodium acetate and 0.05 M with respect to trisodium nitrilo triacetate is filled in five Mariette flasks which are connected respectively with feed holes 12c5 1209. l M hydrochloric acid is filled into the remaining five Mariotte flasks which are in connection with the anode compartment and with respective feed holes 12c1ti- 12013.

By adjusting the height of the air inlet in each Mariette flask, the amount of feed is so regulated that for each separation channel exactly 0.2 ml. per minute of liquid is delivered and 3.2 ml. per minute are delivered into each electrode compartment. The ends of the glass tubes 31 of the withdrawal system are placed in the outlet holes 12d1ll2d13 1 mm. from the bottom thereof. Then the aspirator is set in motion and adjusted to approximately 100 mm. pressure.

When the withdrawal system is ready, the feed is dropped into the feed holes. The electrodes are now con nected to a source of DC. current delivering v. whereby a current of 2 amps. is obtained. After a short initial period of several minutes, separation begins. As soon as it has begun, the pre-cut is discarded and the pure solutions are collected in the vacuum sample changers. Pure cobalt and copper solutions emerge from the separation channels through outlet holes 12113 and ll2dil0 respectively. The flow of water in the cooling system is to be adjusted so as to maintain a temperature of 30 C. in the separation chamber.

The same results are obtained if exactly 0.3 ml. of feed is delivered into all the channels and also if the temperature is kept at 50 C.

What I claim is:

1. A process for concentrating the ions of at least one metal, comprising dissolving material containing said at least one metal in an ionizing solvent, placing the solution thus formed in the space between an anode and a cathode, establishing between said anode and said cathode and through said ionizing solvent a concentration gradient of a complexing base having a steepness of from 10 to 1 mol. per litre per cm., said complexing base being present in an amount of about 1 to 10 times the equimolecular amount of the said at least one metal, the concentration gradient increasing from the anode to the cathode, the complexing base being one which will form metal containing complex anions with the ions of said at least one metal and which takes part in the instantaneous interconversion of the ions of said at least one metal in the ionizing solvent, and while containing the ionizing solvent so as to prevent free convection while permitting ion migration, applying a current through said ionizing solvent from the anode to the cathode for a time suflicient for the complex anions and ions of said at least one metal to reach an equilibrium position with regard to the gradient in the cathode-anode interspace, whereby the metal-containing anions and metal ions of said at least one metal are collected in a small zone in the ionizing solvent in which substantially half of the metal containing ions are in anionic form.

2. A process for concentrating the ions of a pltuality of metals, comprising dissolving material containing said spaassr metals in an ionizing solvent, placing the solution thus formed in the space between an anode and a cathode, comprising establishing between said anode and said cathode and through said ionizing solvent a concentration gradient of at least one complexing base having a steepness of from lto 1 mol. per litre per cm., said compleXing base being present in an amount of about 1 to times the equimolecular amounts of the said metals, the concentration gradient increasing from the anode to the cathode, the complexing base being one which will form metal containing complex anions with the ions of said metals and which takes part in the instantaneous interconversion of the ions of said metals in the ionizing solvent, and while containing the ionizing solvent so as to prevent free convection while permitting ion migration, applying a current through said ionizing solvent from the anode to the cathode for a time suflicient for the complex anions and ions of said metals to reach equilibruim positions with regard to the gradient in the cathode-anode interspace, whereby the metal-containing anions and metal ions of said metals are collected in a plurality of small zones in the ionizing solvent in which substantially half of the metal containing ions are in anionic form, said zones being spaced from each other in the anode-cathode interspace, and mechanically separating the fluid in each zone from the fluid in the other zones.

3. A process for concentrating the ions of a plurality of metals, comprising dissolving material containing said at least one metal in an ionizing solvent, placing the solution thus formed in the space between an anode and a cathode, establishing between said anode and said cathode and through said ionizing solvent concentration gradient of a complexing base having a steepness of from l0 to 1 mol. per litre per cm., said complexing base being present in an amount of about 1 to 10 times the equimolecular amounts of the said metals, the concentration gradient increasing from the anode to the cathode, the complexing base being one which will form metal containing complex anions with the ions of said metals and which takes part in the instantaneous interconversion of the ions of said metals in the ionizing solvent, and while containing the ionizing solvent so as to prevent free convection while permitting ion migration, applying a current through said ionizing solvent from the anode to the cathode for a time suflicient for the complex anions and ions of said metals to reach equilbrium positions with regard to the gradient in the cathode-anode interspace, whereby the metal-containing anions and metal ions of said metals are collected in a plurality of small zones in the ionizing solvent in which substantially half of the metal containing ions are in anionic form, said zones being spaced from each other in the anode-cathode interspace, and mechanically separating the fluid in each zone from the fluid in the other zones.

4. A process for concentrating and separating the ions of a plurality of metals, comprising dissolving material containing said at least one metal in an ionizing solvent, placing the solution thus formed in the space between an anode and a cathode, establishing between said anode and said cathode and through said ionizing solvent concentration gradients of a plurality of complexing bases, each concentration gradient having a steepness of from 10' to 1 mol. per litre per cm., said complexing bases being present in amounts of about 1 to 10 times the equimolecular amounts of the said metals, the concentration gradients increasing from the anode to the cathode, the complexing bases being ones which will form metal containing complex anions with the ions of said metals and which take part in the instantaneous interconversion of the ions of said metals in the ionizing solvent, and while containing the ionizing solvent so as to prevent free convection while permitting ion migration, applying a current through said ionizing solvent from the anode to the cathode for a time sufiicient for the complex anions and ions of said metals to reach equilibrium positions with regard to the gradient in the cathode-anode interspace, whereby the metal-containing anions and metal ions of said metals are collected in a plurality of small zones in the ionizing solvent in which substantially half of the metal containing ions are in anionic form, said zones being spaced from each other in the anode-cathode interspace, and mechanically separating the fluid in each zone from the fluid in the other zones.

5. A process for concentrating the ions of a plurality of difierent metals, comprising dissolving material containing said at least one metal in an ionizing solvent, placing the solution thus formed in the space between an anode and a cathode, establishing between said anode and said cathode and through said ionizing solvent a concentration gradient of at least one complexing base having a steepness of from 10* to 1 mol. per litre per cm., said complexing base being present in an amount of about 1 to 10 times the equimolecular amounts of the said metals, the concentration gradient increasing from the anode to the cathode, the complexing base being one which will form metal containing complex anions with the ions of said metals and which takes part in the instantaneous interconversion of the ions of said metals in the ionizing solvent, and while containing the ionizing solvent so as to prevent free convection while permitting ion migration, applying a current through said ionizing solvent from the anode to the cathode for a time sulficient for the complex anions and ions of said metals to reach equilibrium positions with regard to the gradient in the cathode-anode interspace, whereby the metal-containing anions and metal ions of said metals are collected in a plurality of small zones in the ionizing solvent in which substantially half of the metal containing ions are in anionic form, said zones being spaced from each other in the anode-cathode interspace.

6. A process for concentrating the ions of a plurality of diflerent metals, comprising dissolving material containing said at least one metal in an ionizing solvent, placing the solution thus formed in the space between an anode and a cathode, establishing between said anode and said cathode and through said ionizing solvent a concentration gradient of a complexing base having a steepness of from 10' to 1 mol. per litre per cm, said complexing base being present in an amount of about 1 to 10 times the equimolecular amounts of the said metals, the concentration gradient increasing from the anode to the cathode, the complexing base being one which will form metal containing complex anions with the ions of said metals and which takes part in the instantaneous interconversion of the ions of said metals in the ionizing solvent, and while containing the ionizing solvent so as to prevent free convection while permitting ion migration, applying a current through said ionizing solvent from the anode to the cathode for a time sufiicient for the complex anions and ions of said metals to reach equilibrium positions with regard to said gradient in the cathode-anode interspace, whereby the metalcontaining anions and metal ions of said metals are collected in a plurality of small zones in the ionizing solvent in which substantially half of the metal containing ions are in anionic form, sm'd zones being spaced from each other in the anode-cathode interspace.

7. A process for concentrating the ions of a plurality of different metals, comprising dissolving material containing said at least one metal in an ionizing solvent, placing the solution thus formed in the space between an anode and a cathode, estabiishing between said anode and said cathode and through said ionizing solvent concentration gradients of a plurality of complexing'bases, each concentration gradient having a steepness of from 10" to 1 mol. per litre per cm., said complexing bases being present in amounts of about 1 to 10 times the equimolecular amounts of the said metals, the concen tration gradients increasing from the anode to the cathode, 

1. A PROCESS FOR CONCENTRATING THE IONS OF A LEAST ONE METAL, COMPRISING DISSOLVING MATERIAL CONTAINING SAID AT LEAST ONE METAL IN AN IONIZING SOLVENT, PLACING THE SOLUTION THUS FORMED IN THE SPACE BETWEEN AN ANODE AND A CATHODE, ESTABLISHING BETWEEN SAID ANODE AND SAID CATHODE AND THROUGH SAID IONIZING SOLVENT A CONCENTRATION GRADIENT OF A COMPLEXING BASE HAVING A STEEPNESS OF FROM 10-30 TO 1 MOL. PER LITRE PER CM., SAID COMPLEXING BASE BEING PRESENT IN AN AMOUNT OF ABOUT 1 TO 10**3 TIMES THE EQUIMOLECULAR AMOUNT OF THE SAID AT LEAST ONE METAL, THE CONCENTRATION GRADIENT INCREASING FROM THE ANODE TO THE CATHODE, THE COMPLEXING BASE BEING ONE WHICH WILL FORM METAL CONTAINING COMPLEX ANIONS WITH THE IONS OF SAID AT LEAST ONE METAL AND WHICH TAKES PART IN THE INSTANTANEOUS INTERCONVERSION OF THE IONS OF SAID AT LEAS ONE METAL IN THE IONIZING SOLVENT, AND WHILE CONTAINING THE IONIZING SOLVENT SO AS TO PREVENT FREE CONVECTION WHIL PERMITTING ION MIGRATION, APPLYING A CURRENT THROUGH SAID IONIZING SOLVENT FROM THE ANODE TO THE CATHODE FOR A TIME SUFFICIENT FOR THE COMPLEX ANIONS AND IONS OF SAID AT LEAST ONE METAL TO REACH AN EQUILIBRIUM POSITION WITH REGARD TO THE GRADIENT IN THE CATHOCE-ANODE INTERSPACE, WHEREBY THE METAL-CONTAINING ANIONS AND METAL IONS OF SAID AT LEAST ONE METAL ARE COLLECTED IN A SMALL ZONE IN THE IONIZING SOLVENT IN WHICH SUBSTANTIALLY HALF OF THE METAL CONTAINING IONS ARE IN ANIONIC FORM. 